Device and method for centering and crossing a vascular occlusion

ABSTRACT

A catheter for centrally crossing an occluded blood vessel includes a catheter body having a distal end, a proximal end, and a central passage. A rotatable drive shaft extending through the central passage and has a distal end, a proximal end, and a central lumen. A cutting tip is mounted on the distal end of the rotatable drive shaft and configured to cut through occlusive material when rotated. A plurality of spiral or other flat springs is disposed circumferentially about a distal portion of the catheter body to maintain centering of the catheter and form a passage as the catheter is advanced through a chronic total occlusion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of provisional applicationNo. 62/465,108 (Attorney Docket No. 46306-703.101), filed on Feb. 28,2017, the full disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Chronic total occlusions (CTO) are vascular lesions that block most orall blood flow through a blood vessel. CTO's can occur any in most bloodvessels, including coronary arteries, carotid arteries, iliac arteriesand veins, femoral arteries and veins, and popliteal arteries and veins.Usually CTO lesions will develop over the course several months toyears. Due to this chronic pathology, there usually will be an adequateamount time to for development of collateral vessels to supply blood totissue. These collateral vessels, however, often fail provide enoughblood flow to keep organs alive and support their proper functioning.

Over the years, many catheters have been proposed for the treatment ofCTO's. Of particular interest herein, U.S. Pat. No. 9,060,806, inventedby the inventor herein describes a catheter. The catheter has amotor-driven or other rotatable distal cutter and a plurality oflaterally deployable centering elements. While quite effective, thecentering elements on this design were not always able to maintaincentering when crossing certain hard lesions and the motor-driven orother rotatable distal cutter could be difficult to control under somecircumstances.

For these reasons, it would be desirable to provide improved devices andmethods for crossing vascular occlusions or other blockages formedwithin blood vessels in order to treat the occlusion as well as tocreate pathways for the placement of guidewires, interventional devicesand catheters. In particular, it would be desirable to provide lowprofile devices for creating centered passages through an occlusion witha high degree of control and a reduced resistance to advancement of thedevice. Such devices should be relatively inexpensive to produce andrelatively simple to use. At least some of these objectives will be metby the inventions described herein below.

2. Description of the Background Art

U.S. Pat. No. 9,060,806 has been described above. The following patentsand publications are also of interest: U.S. Pat. No. 6,599,304; U.S.Pat. No. 7,763,012; U.S. Pat. No. 8,021,330; U.S. Pat. No. 8,062,316;U.S. Pat. No. 8,241,315; U.S. Pat. No. 8,361,094; U.S. Pat. No.8,556,926; US2002/0128677; US2005/0038462; US2005/0171572;US2005/0216044; US2006/0074442; US2007/0083193; US2008/0281323;US2009/0270714; US2010/0082051; US2010/0168557; US2011/0022045;US2012/0253186; US2012/0283565; and US2014/0277009.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a catheter forcentrally crossing an occluded blood vessel. The catheter comprises atubular catheter body having a distal end, a proximal end, and a centralpassage therethrough. A rotatable drive shaft extends through thecentral passage of the tubular catheter body and has a distal end, aproximal end, and a central lumen therethrough. A cutting tip is mountedon the distal end of the rotatable drive shaft, and the cutting tip isconfigured to cut through occlusive material, such as plaque, calcifiedplaque, clot, thrombus, and the like, when rotated. The cutting tip hasa passage contiguous with the central lumen of the rotatable driveshaft. As described in detail below, the contiguous passage and lumenallow guidewire placement after the occlusion has been crossed and acentered passage through the occlusion has been created.

The crossing catheters of the present invention have a particularcentering mechanism which accurately centers a distal region of thecatheter as the cutting tip is rotated to create a passage through thevascular occlusion. The centering mechanism is particular beneficial asit has a low “crossing” profile (circumferential width) that allows itto be pushed through the occlusive material but presents a largecircumferential surface area for engaging the vascular wall to minimizethe trauma. More specifically, the centering mechanism comprises aplurality of flat springs, usually flat spiral springs as described inmore detail below, disposed circumferentially about a distal region ofthe tubular catheter body. The flat springs are adapted to elasticallyself-expand from a radially constrained configuration to a radiallyexpanded configuration so that they can be deployed after the catheterhas been advanced to a location near the occlusion in a target bloodvessel. Each flat spring has a (1) wide lateral surface configured toatraumatically engage a wall region of the blood vessel to centrallyalign the tubular catheter body in a lumen in the blood vessel and (2) anarrow distal edge configured to penetrate the occlusion as the catheteris distally advanced. In specific examples, the flat springs are cutfrom a tubular element so that the flat springs are initially portionsof a cylinder and deploy by radially unfolding from the cylinder toextend radially outwardly in a spiral pattern to engage the blood vesselwall.

In preferred embodiments of the present invention, the cutting tip willbe rotated by a manual mechanism allowing the treating physician toadvance the catheter inclusion while manually controlling the cuttingaction of the tip. In particular, the physician will be able to observeprogress of the cutting tip fluoroscopically, and when combined withtactile feedback, the physician can manually control the rate ofadvancement and the rate of rotation of the cutting tip to optimallyadvance the catheter to create the desired center passage through theocclusion. Conveniently, the cutting tip may be manually driven by awheel or spindle disposed in a handle at the proximal end of thecatheter.

The dimensions of the catheter will generally be from 120 cm to 150 cmin length from 5 Fr to 7 Fr (one French (Fr) equals 0.33 mm) indiameter, with specific dimensions depending on the catheter's intendeduse. For example, catheters intended for treating the coronary arterieswill typically have a length in the range from 130 cm to 150 cm and adiameter from about 5 Fr to 7 Fr For peripheral devices, the tubularcatheter body will typically have a length in the range from 120 cm to140 cm and a diameter in the range from 5 Fr to 7 Fr.

The cutting tip may take a variety of configurations. Particularlypreferred is a cutting tip which includes at least one cutting loop,often two cutting loops, extending in the distal direction from a distalend of the cutting tip. For coronary applications, a single cutting loopmay be radially offset from a guidewire port axially aligned with thepassage through the cutting tip or two cutting loops may be disposedsymmetrically on opposite sides of the guidewire port. For peripheralapplications, the cutting loop may be centered on the cutting tip andthe passage through the cutting tip will be inclined or radially offsetfrom the central axis of the cutting tip to direct a guide wire awayfrom the cutting loop or a pair of cutting loops may be symmetricallypositioned on the cutting tip as with the coronary designs.

In other aspects of the present invention, each of the plurality ofspiral or other flat springs may have a Ω-shape with a base portionattached to the tubular catheter body and a loop portion extendingradially away from the tubular catheter body. In other cases, theplurality of spiral flat springs will consist of three spiral flatsprings. In such cases, the three spiral flat springs will usually bespaced circumferentially apart by 120°. Conveniently, the spiral flatsprings may be fabricated by laser cutting or otherwise patterning atubular blank formed from an elastic material, usually an elastic metal,more usually a superelastic metal, such as a nickel-titanium alloy (e.g.Nitinol® alloy).

In a second aspect of the present invention, a method for centrallycrossing an occluded blood vessel comprises advancing a catheter throughan occlusion in the blood vessel. A cutting tip is rotated orrotationally oscillated on a distal end of the catheter to cut or abradea path through the occlusive material as the catheter is advanced. Inorder to center the catheter during the cutting procedure, a pluralityof spiral or other flat springs are deployed or unfurled from a distalportion of the tubular catheter body. A wide lateral surface on each ofthe flat springs atraumatically engages a wall region of the bloodvessel to centrally align a distal region of the catheter body in alumen of the blood vessel while a narrow distal edge of each of the flatsprings penetrates through the occlusion as the catheter is advanced,typically compressing and/or cutting the plaque or thrombus to enlargethe passage initially formed by the cutting tip.

In specific embodiments of the method, the cutting tip is manuallyoscillated or rotated, typically by rotating a cylinder or wheel on ahandle attached to a proximal end of the catheter. Unfurling theplurality of spiral flat springs typically comprises releasing thespiral flat springs from radial constraint so that they can elasticallyself-expand, typically by advancing a distal portion of the catheterfrom a sheath or guiding catheter which constrains the spiral flatsprings as the catheter prior to advancing the cutting tip through theocclusion.

In further specific embodiments, the centering catheter may be used toplace a guidewire through the passage created by the catheter. Forexample, the catheter may carry and optionally utilize a guidewire forinitial placement. That guidewire can also be used to assist inadvancing the catheter across an occlusion. After the catheter hascrossed the occlusion, the guidewire may be left in place through theocclusion for advancement of further interventional and/or diagnosticdevices. In other instances, however, the centering catheter can beadvanced to, but not through, an occlusion, and used as a platform foradvancing guidewires and other devices into the occlusion, The centeringcatheter can provide an excellent platform for advancing tools intoand/or through the center of an occlusion. In still other cases, asecond guidewire may be exchanged for an initial placement guidewirewhen a guidewire with different characteristics is needed.

In some instances, while the catheter remains centered, a guidewire orother tool can be advanced and penetrated through a distal face of theinclusion. After penetration of the distal face, the cutting cathetercan be then be advanced. In still other embodiments, the catheter can beadvanced using the cutting tip until a proximal face of the occlusion isapproached. Before cutting through the proximal face of the occlusion,however, guidewire can be deployed from the centering catheter andpassed through the distal face of the occlusion. The cutting andcentering catheters of the present invention are thus useful for a widevariety of specific protocols requiring or benefiting from a centralalignment of the catheter with the occlusion.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates a first embodiment of a catheter for centering andcrossing a vascular occlusion constructed in accordance with theprinciples of the present invention.

FIG. 2 is a longitudinal cross-sectional view of a distal portion of thecatheter for centering and crossing a vascular occlusion of FIG. 1 shownwith a centering cage in a radially expanded configuration.

FIG. 3A is an alternative view of the distal portion of the catheter forcentering and crossing a vascular occlusion of FIG. 1 shown with thecentering cage in a radially constrained configuration.

FIG. 3B illustrates a distal portion of an alternative embodiment of acatheter for centering and crossing a vascular occlusion constructed inaccordance with the principles of the present invention of a typeparticularly intended for treating occlusions in the peripheral;vasculature.

FIG. 4 illustrates an alternative cutting tip with two cutting loops anda fluted distal cutting surface.

FIG. 5 is a front view of distal portion of the catheter for centeringand crossing a vascular occlusion of FIG. 1 shown with a centering cagein a radially constrained configuration.

FIG. 6 is a front view of distal portion of the catheter for centeringand crossing a vascular occlusion of FIG. 1 shown with a centering cagein a radially expanded configuration.

FIG. 7 is a partial cross-sectional view of a proximal handle of thecatheter for centering and crossing a vascular occlusion of FIG. 1.

FIG. 8 is a detailed cross-sectional view of a distal end of theproximal handle of FIG. 7 taken along line 8-8 of FIG. 7.

FIGS. 9A-9C illustrate the use of the catheter of FIG. 1 for centeringand crossing a vascular occlusion and thereafter advancing a guidewirethrough the path created.

FIG. 10 illustrates an alternative embodiment of the centering andcrossing catheter of the present invention having a cutting tip that maybe distally advanced relative to a centering cage to facilitateadvancement of the catheter through tortuous vasculature.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a catheter 10 for centering and crossingvascular occlusions comprises a catheter body having a distal endportion 12 and a proximal end 14 having a proximal handle 16 thereon. Arotatable cutting tip 18 is located at a distal tip of the distal endportion 12 and includes a single cutting loop 20 which may be rotated asdescribed in more detail below. A centering cage 22 circumscribes thedistal end portion 12 to maintain centering of the distal end portion 12within a vascular lumen as the catheter 10 is advanced therethrough. Inparticular, the centering cage 22 includes a plurality (three asillustrated) of planar, usually spiral springs 24. The spiral springsare preferably formed by cutting or otherwise patterning a cylindricaltube 26, where the entire tube may then be secured to the distal endportion 12 of the catheter 10. The cylindrical tube 26 will typically beformed from nitinol or other elastic metal and will be heat set so thatthe individual spiral springs 24 are in their radially expandedconfiguration in the absence of a radial constraint, such as a deliverysheath, guide catheter, or the like.

Referring now also to FIGS. 2 and 3A, the catheter 10 includes an outershaft 30 and an inner drive shaft 32. The inner drive shaft 32 isconcentrically disposed within a luminal passage of the outer shaft andis rotatable therein as will be described in more detail below. Theinner drive shaft 32 also has a lumen 34 which is configured toaccommodate a guidewire GW as well as for other purposes, such asinfusion, suction, and the advancement of other interventional tools.

The cutting tip 18 has a central passage 36 which is aligned andcontiguous with the lumen 34 of the inner drive shaft. The centralpassage 36 has a distal opening 38 through which a guidewire or otherelement, tool, or component may be advanced. The cutting tip 18 isfixedly attached to a distal end of the inner drive shaft 32 so thatrotation of the inner drive shaft will cause rotation of the cutting tip18 as well as the cutting loop 20. A retaining ring 40 is provided tohold the inner drive shaft 32 within the central luminal passage of theouter shaft 30.

While the central passage 36 of the cutting tip 18 will typically beaxially aligned with the lumen 34 of the inner drive shaft, in otherembodiments, such as those intended for peripheral use as shown in FIG.3B, a cutting tip 118 will have a centrally aligned cutting loop 120which has a passage 136 which is inclined or offset relative to itslongitudinal axis so that the distal opening 138 deflects the guidewireaway from the cutting loop 120. All other components and numbering shownin FIG. 3B are identical to those in the previous figures.

Referring now to FIG. 4, a catheter 100 according to the presentinvention may have an alternative cutting tip 118 design with a pair ofcutting loops 20 a and 20 b disposed on either side of a distalguidewire port 112, typically being placed symmetrically about the port.In addition a plurality of flutes 154 may be formed in a distal surfaceof the cutting tip 118 to further aid in cutting through plaque or clotas the tip is rotated or rotationally oscillated at the catheter isadvanced. A centering cage 122 may be formed with a plurality of spiralor other flat springs 124 having flat surfaces 128 when deployedradially outwardly to engage the vessel wall as the catheter isadvanced. While centering cage 12 is similar to cage 22 describedpreviously, cage 124 may have a shorter length to facilitate advancementthrough tortuous regions of the vasculature, particularly the coronaryvasculature. An outer shaft 130 and an inner drive shaft 132 may haveconstructions similar or identical to the constructions describedpreviously for outer shaft 30 and inner drive shaft 32.

Referring now to FIGS. 5 and 6, when radially constrained, the spiralcentering springs 24 will generally be collapsed within an envelopedefined by the cylindrical tube 26, as shown in FIG. 5. When releasedfrom constraint, in contrast, each of the three spiral centering springs24 a, 24 b and 24 c will radially open to define flat surfaces 28 havingan effective diameter shown in broken line. The particular contours andflat surfaces defined by each of the spiral centering springs can bedetermined by thermal setting of the nitinol or other shape memory metalduring fabrication of the centering cage 22. As also observed in FIG. 6,the leading edge of each of the spiral centering springs 24 has a verylow profile which allows the centering springs to be advanced throughocclusive material with a reduced resistance to pushing.

The handle 16 is best illustrated in FIGS. 7 and 8. The handle 16 has anose 42 which is attached to the proximal end of the outer shaft 30 ofthe catheter body. The outer shaft is fixedly attached so that the outerwill be prevented from rotating relative to the handle. In contrast, theinner drive shaft 32 is attached to a wheel or spindle 44 which isrotatably mounted in the handle 16 to permit manual rotation of thewheel or spindle relative to the handle. Rotation of the wheel orspindle 44, in turn, will rotate the inner drive shaft 32 which and inturn rotates the distal cutter 18 and cutting loop 20. A proximal end ofthe inner drive shaft 32 (located proximately of the wheel or spindle44) passes through a bearing connector 48 and is received within atransition tube 46 which leads to a luer fitting 50 at a proximal end ofthe handle. The luer and transition tube will be rotationally fixedwithin the handle, and the proximal end of the inner drive shaft 32 anddistal end of the transition tube 46 will form a rotating seal in thebearing connector. It will be appreciated that guidewires and otherinterventional elements may be introduced through the luer 50 and lumenof the inner drive shaft 32 so that they may be advanced to the distaltip of the catheter and out through the distal opening 38 of the cuttingtip 18.

Referring now to FIGS. 9A through 9D, the catheter 10 for centering andcrossing occlusions may be advanced through a chronic total occlusionCTO in a blood vessel BV, as illustrated. The distal end portion 12 ofthe catheter 10 is initially advanced so that the cutting loop 20 liesimmediately proximal to a proximal surface of the chronic totalocclusion CTO. The user then manually rotates the cutting tip 18 andcutting loop 20 while advancing the catheter to penetrate through theproximal face of the occlusion and begin to create a central passagetherethrough. The spiral centering springs 24 of the centering cage 22engage the inner walls of the blood vessel and maintain centering of thedistal region 12 of the catheter as the catheter is advanced. Asdescribed previously, the flat surfaces of the springs atraumaticallyengage the vessel wall while the low width of each spring allows thecentering cage to pass through the occlusive material with reducedresistance. The catheter can be incrementally advanced as the usermanually rotates the cutting tip and observes the progressfluoroscopically. The procedure may be complete when the distal tip ofthe catheter passes through a distal face of the occlusion, as shown inFIG. 9C. After the catheter has reached the position shown in FIG. 9C, aguidewire GW may be placed, catheter 10 is removed and/or otherinterventional procedures may be performed.

Referring now to FIG. 10, catheter 100 having the cutting tip 118illustrated in FIG. 4 may be further modified to allow axial advancementand retraction of the cutting tip relative to the centering cage 122. Inparticular, a thumb slide 160 may be positioned in a slot 164 in a wallof handle 114, preferably located distal to the wheel 144. The thumbslide is coupled to the outer member 130 so that by sliding the thumbslide axially, as indicated by arrow 162, the outer member and itsdistally attached centering cage 122 may be axially advanced andretracted, typically over a range from 3 cm to 4 cm, relative to theinner member 132 and cutting tip 118, as indicated by arrow 164. Theability to de-couple a distal segment of inner member shaft and theattached cutting tip 118 is a significant advantage when advancing thecatheter through tortuous vasculature, such as coronary vasculature,where the cutting tip and distal inner member shaft may be firstadvanced past a tight and/or narrow curve in the vasculature with thecentering cage 122 being separately advanced thereafter coaxially overthe inner member shaft.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

What is claimed is:
 1. A catheter for centrally crossing an occludedblood vessel, said catheter comprising: a tubular catheter body having adistal end, a proximal end, and a central passage therethrough; arotatable drive shaft extending through the central passage of thetubular catheter body and having a distal end, a proximal end, and acentral lumen therethrough; a cutting tip mounted on the distal end ofthe rotatable drive shaft and configured to cut through occlusivematerial when rotated, said cutting tip having a passage contiguous withthe central lumen of the rotatable drive shaft; a plurality of flatsprings disposed circumferentially about a distal portion of the tubularcatheter body and adapted to elastically self-expand from a radiallyconstrained configuration to a radially expanded configuration whereineach flat spring has (1) a wide lateral surface configured toatraumatically engage against a wall region of the blood vessel tocentrally align said tubular catheter body in a lumen of the bloodvessel and (2) a narrow distal edge configured to penetrate theocclusion as the catheter is distally advanced; and a handle at theproximal end of the tubular catheter body.
 2. A catheter for centrallycrossing an occluded blood vessel as in claim 1, wherein the flatsprings are configured to self-expand in a spiral pattern.
 3. A catheterfor centrally crossing an occluded blood vessel as in claim 1, whereintubular catheter body has a length in the range from 120 cm to 150 cmand a diameter from 5 Fr to 7 Fr.
 4. A catheter for centrally crossingan occluded blood vessel as in claim 1, further comprising a manualrotation device attached to the rotatable drive shaft.
 5. A catheter forcentrally crossing an occluded blood vessel as in claim 3, wherein themanual rotation device comprises a rotating cylinder in the handle.
 6. Acatheter for centrally crossing an occluded blood vessel as in claim 1,wherein the cutting tip includes at least one cutting loop extending ina distal direction from a distal end of the cutting tip.
 7. A catheterfor centrally crossing an occluded blood vessel as in claim 6, whereinthe at least one cutting loop extending in a distal direction from thedistal end of the cutting tip is radially offset from the passage in thecutting tip.
 8. A catheter for centrally crossing an occluded bloodvessel as in claim 6, wherein the passage in the cutting tip is alignedwith a central axis of the rotatable drive shaft and the at least onecutting loop is radially offset from the central axis.
 9. A catheter forcentrally crossing an occluded blood vessel as in claim 6, wherein theat least one cutting loop is aligned with a central axis of therotatable drive and the passage in the cutting tip is radially offsetfrom the central axis.
 10. A catheter for centrally crossing an occludedblood vessel as in claim 6, wherein the at least one cutting loop isaligned with a central axis of the rotatable drive and the passage inthe cutting tip is radially offset from the central axis.
 11. A catheterfor centrally crossing an occluded blood vessel as in claim 6, whereinthe cutting tip includes at least two cutting loops extending in adistal direction from a distal end of the cutting tip.
 12. A catheterfor centrally crossing an occluded blood vessel as in claim 1, whereinthe cutting tip has a fluted distal surface.
 13. A catheter forcentrally crossing an occluded blood vessel as in claim 1, wherein eachof the plurality of flat springs has an Ω-shaped profile with a baseportion attached to the tubular catheter body and a loop portionextending radially away from the tubular catheter body.
 14. A catheterfor centrally crossing an occluded blood vessel as in claim 1, whereinthe plurality of flat springs consists of three flat springs.
 15. Acatheter for centrally crossing an occluded blood vessel as in claim 14,wherein the three spiral flat springs are spaced circumferentially apartby 120°.
 16. A catheter for centrally crossing an occluded blood vesselas in claim 1, wherein the rotatable drive shaft is axially translatablerelative to the tubular catheter body so that the cutting tip and thetubular catheter body can be axially repositioned relative to eachother.
 17. A catheter for centrally crossing an occluded blood vessel asin claim 16, further comprising a thumb slide on the handle forselectively repositioning the tubular catheter body relative to thehandle and the rotatable drive shaft.
 18. A method for centrallycrossing an occluded blood vessel, said catheter comprising: advancing acatheter through an occlusion in the blood vessel; and rotating orrotationally oscillating a cutting tip mounted on a distal end of thecatheter to cut through occlusive material as the catheter is advanced;wherein a plurality of flat springs deploy laterally outwardly to (1)atraumatically engage a wide lateral surface of each flat spring againsta wall region of the blood vessel to centrally align said catheter in alumen of the blood vessel as the catheter is advanced, and (2) penetratea narrow distal edge on each spiral flat spring through the occlusion tocreate a passage through the occlusion as the catheter is advanced. 19.A method for centrally crossing an occluded blood vessel as in claim 18,wherein rotating or rotationally oscillating the cutting tip comprisesmanually rotating or rotationally oscillating the tip.
 20. A method forcentrally crossing an occluded blood vessel as in claim 19, whereinmanually rotating or rotationally oscillating the tip comprises rotatingor rotationally oscillating a cylinder on a handle attached to aproximal end of the catheter.
 21. A method for centrally crossing anoccluded blood vessel as in claim 18, wherein the flat springs comprisespiral flat springs and wherein said spiral flat springs self-deployfrom a distal portion of the catheter after releasing the flat springsfrom radial constraint so that they elastically self-expand.
 22. Amethod for centrally crossing an occluded blood vessel as in claim 21,wherein releasing the flat springs from radial constraint comprisesadvancing the distal end of the catheter beyond a distal end of a guidecatheter.
 23. A method for centrally crossing an occluded blood vesselas in claim 18, further comprising withdrawing the catheter and thecutting tip over a guidewire disposed in a central passage of thecatheter and the cutting tip to leave the guidewire in the blood vessellumen.
 24. A method for centrally crossing an occluded blood vessel asin claim 23, wherein the catheter and the cutting tip had been advancedfully through an occlusion prior to being retracted to leave theguidewire in place fully through the occlusion.
 25. A method forcentrally crossing an occluded blood vessel as in claim 23, wherein thecatheter and the cutting tip had been advanced partially through anocclusion prior to being retracted, further comprising advancing theguidewire through a remaining portion of the occlusion.
 26. A method forcentrally crossing an occluded blood vessel as in claim 23, wherein thecatheter and the cutting tip had been advance to a proximal face of anocclusion prior to being retracted, further comprising advancing theguidewire through the occlusion.